My trees are being blown too fast and my grass is not affected by my wind physics after a few seconds
As your file is not added so I cannot tell much but still i can give you some idea. I hope your grass is using a particle system and it it is true then you can just increase the strength of wind on grass instead of increasing it overall and for that just go to field weights in particle(Hair) settings and increase the wind strength to 5 - 10 or as high as you need.
Let me know if this works for you.
If not then comment it down and i will try to give you another fix